Abstract

We present experimental results highlighting the physical mechanism responsible for the initial spectral broadening of femtosecond Ti:Sapphire pulses in a highly birefringent microstructured fiber having a small effective area. By rotating the input polarization and varying the injected power while monitoring the resulting changes in the output spectrum, we are bringing clear evidences that the initial broadening mechanism leading to a broadband supercontinuum is indeed the fission of higher-order solitons into redshifted fundamental solitons along with blueshifted nonsolitonic radiation.

Figures (5)

SEM images of the 2 m long MS fiber used for the experiment (left) and a detailed view of its central region (right). The outer diameter of the fiber is 125 µm and the elliptical core has dimensions 1.3µm×2.2 µm.

Generated supercontinua along the two eigenpolarization axes of the fiber shown in Fig. 1. The upper spectrum was generated along the fast axis while the lower spectrum was generated along the slow axis. The dip on those spectra indicates that the fast axis has a ZDW of 625 nm while the slow axis has a ZDW of 645 nm.

(529 KB) Evolution of the generated spectrum as the injected intensity is increased. The pump wavelength was λ=740 nm, the pulse duration ΔtFWHM=127 fs and the polarization was oriented along the slow axis of the fiber. On the right is shown a detailed view of the supercontinuum generated at 91 GW/cm2 of injected intensity (Po=2.7 kW).

(508 KB) Evolution of the generated spectrum as the injected intensity is increased. The pump wavelength was λ=758 nm, the pulse duration ΔtFWHM=192 fs and the polarization was oriented along the slow axis of the fiber. On the right is shown a detailed view of the supercontinuum generated at 56 GW/cm2 of injected intensity (Po=1.7 kW).

Evolution of the generated spectrum as the input polarization is rotated. The 0° position was aligned with the slow axis of the fiber. The input pulses had a wavelength λ=758 nm, the pulse duration ΔtFWHM=192 fs and the injected intensity was 60, 20 and 10 GW/cm2 for a, b and c respectively.